This invention relates to a temperature compensating circuit for compensating the operation of an electronic circuit such as an oscillation circuit having a temperature characteristic, for example, and an electronic device and radio unit having a temperature compensating function.
Generally, in an electronic device constructing a terminal device or a base station for mobile communication, an oscillation circuit such as a synthesizer is provided. This type of oscillation circuit generally uses a reference oscillator including a quartz oscillator. The quartz oscillator generally has a temperature characteristic which exhibits a cubic curve, for example. Therefore, in order to attain stable oscillation frequencies, it is indispensable to correct the operation of the oscillation circuit while taking the temperature characteristic of the quartz oscillator into consideration.
In the prior art, for example, an oscillation circuit having a temperature correcting or compensating function and using a thermostatic device which is called a temperature compensated crystal oscillator (TCXO) as the quartz oscillator is used. However, since the quartz oscillator using the thermostatic device is generally large and expensive, the size of the oscillation circuit will become large and the cost thereof will be high.
An oscillation circuit for correcting the oscillation frequency according to a variation in temperature by changing the bias voltage of the oscillation circuit by use of a combination of a temperature sensor such as a thermistor and a variable capacitance element is known. Since this type of circuit does not use an expensive quartz oscillator, the cost of the oscillator circuit is lowered and the size thereof can be made small. However, in the oscillation circuit using the temperature sensor to attain temperature compensation, it is difficult to attain precise temperature compensation over a wide temperature range due to an influence of the detection error of the temperature sensor and a variation thereof and, as a result, a stable oscillation circuit cannot be provided.